The present invention relates to an IR radiant heater having at least one two-dimensional (planar) carbon filament in a housing that is transparent or at least partially transparent to IR radiation.
Such an IR radiator is realized according to European published patent application No. EP 0 881 858 A2 with a single filament arranged in a round tube and in German published patent applications Nos. DE 44 38 871 A1 and DE 44 19 285 A1 with several carbon filaments arranged next to each other. The carbon materials used there consist of parallel carbon fibers, which are connected by resin. These structures are carbonized and graphitized before installation in the radiator.
The radiator disclosed in EP 0 881 858 is not suitable for uniform two-dimensional radiation. DE 44 38 871 and DE 44 19 285 relate to the use of comparable filaments, but with the goal of achieving two-dimensional (2D) radiation.
However, the carbon filaments disclosed in these documents cannot be assembled into arbitrary two-dimensional heating elements, because the material can have only an elongated and constant width arrangement. The arrangements shown in DE 44 38 871 can realize this configuration, but neither uniform radiation intensities, nor such bent or round shapes, or even 3D shaped structures, can be realized.
Even the arrangement shown in DE 44 38 871, FIG. 5a exhibits a considerable variation in temperature, and thus of the radiated output per unit of length in the bands located at the edge, due to the different lengths of the different fibers. Arrangements with a plurality of narrow bands, like those in DE 44 19 285, require a plurality of complicated and expensive contacts for the individual bands relative to each other.
However, such carbon bands cannot be arranged in arbitrary two-dimensional patterns, because the bands only permit minimal deviations from a parallel arrangement. Bands can be arbitrarily formed perpendicular to their two-dimensional configuration. However, such arrangements lack the two-dimensional character of a radiating surface.
The present invention also relates to the use of CFC material for radiant heaters.
Japanese published patent application No. JP 7-161725 A1 describes cutting out a heating pattern from planar material, wherein silicon carbide (SiC) is used. The SiC heating element there is located in an open housing made of quartz glass, on which a graphite disk (see FIG. 1, No. 8) is placed on the side used for the heat treatment. The graphite disk is heated by the SiC heater and then secondarily warms the material. Such heating elements made of SiC or graphite are brittle and rigid, so that they are very sensitive to fracture. The heating element is also electrically contacted rigidly by screws, so that heat expansion introduces there an additional risk of fracture. To guarantee sufficient mechanical strength in such heating elements, these must be constructed very large. Due to the low electrical resistance present there, very high currents flow during operation at low voltages. This requires complicated power-grid supply circuits and the electrical supply lines can be guided into a vacuum-tight quartz body only with difficulty. For this reason, the quartz glass housing there also has an open shape.
European Patent No. EP 0 899 777 B1 describes a carbon heating device with a heating device member made of carbon fiber bundles extending in a longitudinal direction and interwoven with each other, such as a band or wire shape. These interwoven carbon fiber bundles are expressly not by graphite expressly not converted into CFC by graphite. Thus, these bundles remain very flexible, and the risk of brittle fracture is avoided. The described wire-shaped or band-shaped heating device elements have a high electrical resistance, so that the heating device can be designed to operate at common voltages. Due to the very low number of fibers in the band, however, even at maximum output only a rather small current of a few amperes flows, so that overall the electrical output of such a unit turns out to be rather small at 30 kW/m2. 
The heating device element is laid in channels, which have been milled in a first quartz plate. Then the heating device is sealed by a second quartz plate, which is laid on the first plate and connected to it. The connection is realized by placing a weight of 10 kg and a heating process, in which the entire device is heated to 1450° C. for 3 hr. The resulting connection of the two quartz plates is not a continuous weld and, after long-term operation, gaps can appear due to mechanical and-thermal loads.
According to U.S. Pat. No. 6,584,279 B2, an IR radiator with an electrical output of up to 28 kW/m2 is obtained with braided carbon fibers.
In braking technology, carbon fiber-reinforced carbon (CFC) disks made of CFC material or Si-impregnated CFC are used.